In normal blending operations, fibers are fed by means of lift aprons from hoppers into weigh pans. Positioned below the lift aprons are weigh pans that are equipped with counter balance arms that may be set to control the amount of fibers deposited on a conveyor belt positioned therebelow. When all of the weigh pans are loaded with a predetermined weight of fibers, a signal is produced that causes the weigh pans to simultaneously drop the fibers onto the conveyor belts. When the fibers are being dropped onto the conveyor belts, a drive mechanism associated with the conveyor is energized causing the conveyor to advance a predetermined distance. Normally, this distance is at least the separation of the weigh pans. One particular apparatus for feeding textile fibers utilizing weigh pans is disclosed in U.S. Pat. No. 3,132,709 granted on May 12, 1964 to K. G. Lytton. Usually there are from four to six weigh pans provided over the conveyor, however, there can be any number depending on the particular blend being desired.
In order to ensure that the particular weigh pans are dropping the desired amount of fibers on each drop, an operator normally checks the weight by collecting the fibers produced by a particular drop and weighing such on a scale. This, of course, is very time consuming and is only as accurate as the care taken by the person performing the weighing operation in collecting all of the fibers that were dropped, and upon the frequency of the weigh operations. If the weigh pan, for example, malfunctions soon after the fibers are manually weighed, then a blend would be out of tolerance until the next weighing takes place.
Apparently, there have been many attempts to solve the problem of monitoring the flow of fibers from a plurality of hoppers to a conveyor in order to control the blend, however, applicant is not aware of any such devices that have been made commercially available on the market. An example of such a device is disclosed in U.S. Pat. No. 3,918,539 which discloses a weighing system for the weigh pans. In U.S. Pat. No. 3,494,507, there is disclosed still another metering apparatus for use in conjunction with fiber feeding devices.
U.S. Pat. No. 3,985,266 discloses apparatus for controlling the feed rate and batch size of material being fed. This device takes into consideration the weight of the fibers being supplied as well as the speed of the conveyor. Other patents of similar interest include U.S. Pat. Nos. 3,939,929, 4,000,541, 3,889,319, 3,960,225, 3,957,126, and 4,038,531.